The present invention is directed to collecting and characterizing gas-borne particles, particularly to the integration of an entire suite of discrete laboratory aerosol handling and characterization techniques into a single device. More particularly, this invention is directed to an xe2x80x9caerosol lab-on-a-chipxe2x80x9d (ALOC) device, analogous to a microelectromechanical system (MEMS) device formed in silicon, by processes such as those described in U.S. Pat. Ser. Nos. 5,189,777, 5,331,236, and 5,455,547, and/or by advanced electrochemical and lithographic processes (Lithographic Galvanoforming Abforming or xe2x80x9cLIGAxe2x80x9d) such as are described in U.S. Pat. Ser. Nos. 5,378,583, 5,631,514, and 5,917,260, all herein incorporated by reference.
These so-called MEMS or LIGA techniques are well known in the art, being similar to those used to produce the now familiar integrated circuit (IC), and have been shown to be capable of producing sub-millimeter to micron scale electrical/mechanical devices on a substrate of silicon. This technology has been exploited herein to integrate a variety of known aerosol processing techniques into a single package which is at once compact, rugged, self-contained, and inexpensive to manufacture. For convenience therefore, these LIGA and MEMS techniques will be collectively referred to throughout the remainder of the instant application as xe2x80x9cmicro-machiningxe2x80x9d techniques. In like manner, devices fabricated using these techniques shall likewise be referred to as xe2x80x9cmicro-machines.xe2x80x9d
A typical problem facing the aerosol field is that of collecting and characterizing gas-borne particles. As used here, the term xe2x80x9caerosolxe2x80x9d refers to liquid or solid particles that are suspended in a gas (e.g., air). The particles may be anthropogenic (such as smog, fly ash, or smoke) or naturally occurring (such as pollens, dust, or mists). Sometimes the characterization of these gas-borne particles can be performed in situ (i.e., while the particles remain suspended in a gas), while in extractive techniques these particles are collected and then deposited onto a solid substrate or into a liquid for the purpose of subsequent physical or chemical analysis. Hereinafter, aerosol characterization is defined as the determination of the distribution of the size or shape, the chemical or biological composition, or any physical or chemical property of the suspended particles comprising the aerosol.
A large number of aerosol characterization techniques have been developed in the past. Examples of in situ instruments include those which infer particle size based on measurements of particle light scattering, (e.g. optical particle sizers or phase Doppler particle analyzers), on measurements of particle inertia (e.g. an aerodynamic particle sizer) or on measurements of particle electric mobility (e.g. differential mobility analyzers and electrical aerosol analyzers). Consequently, in situ techniques can provide detailed aerosol size distribution data (mass or number of suspended particles as a function of particle size per volume of gas). On the other hand, simple extractive instruments (e.g., jet impingers, jet impactors, cyclones, and filters) deposit particles onto a substrate with little or no size discrimination. For example, impactors and cyclones typically collect most particles larger than some characteristic diameter, while most smaller particles pass through. When detailed size distribution information is desired with these devices, the incoming aerosol first must be preconditioned in order to sort the particles according to size. In some cases, this sorting is accomplished by using a series of extractive devices that collect progressively smaller particles; examples include cascade inertial impactors or cascade cyclones.
The aerosol collection/analysis task is further complicated when only particles in a specific size interval are of interest. One such example is that of bioaerosols, which include air-borne pollens, viruses, or bacteria. Bioaerosols can result from natural processes (e.g., pollen releases by plants), or from human activities by inadvertent (e.g., in operating rooms, communicable diseases) or intentional (e.g., agricultural or battlefield) release. For example, bacteria typically range in size between about 1 and 5 microns, and it would be desirable to collect only particles in this size range to analyze airborne bacteria. Further complications to aerosol characterization arise when the concentration of particles of interest is very low (where particle concentration is given by the number of particles per unit volume of gas). Bioaerosols can again be used as an example; here the challenge is to separate bioaerosols from a potentially high concentration of background aerosol, ideally by removing the background particles and enriching the concentration of desired particles.
For aerosol characterization problems, the ideal aerosol instrument would be one which could accurately collect, classify, concentrate (enrich), and characterize particles in a variety of environments. The ideal instrument would also be compact, rugged, lightweight, and inexpensive, and would have low power consumption requirements. This instrument would provide a complete description of the aerosol size distribution, along with a determination of the particle chemical, physical, or biological composition distribution. Unfortunately, this ideal instrument does not currently exist. Currently, a complete description of an unknown aerosol relies on simultaneous or consecutive measurements using a combination of bench-top in situ or extractive instruments. Independent analytic techniques are often combined to help remove inherent ambiguities which result from the fact that most techniques do not directly measure true particle size, but in fact infer size from a direct measurement of some particle physical response. Each of these instruments must provide its own gas-handling, sensor, signal processing, and data acquisition capabilities (although many are now linked to computers); consequently, most of these systems are not compact, require line AC power, and are expensive. If more than one instrument is operated simultaneously, there always is the question as to whether all are analyzing the same aerosol due to potential upstream sampling and transport discrepancies.
The present invention provides one solution in the search for the ideal aerosol diagnostic tool, and involves an aerosol lab-on-a-chip (ALOC) in which a variety of aerosol collection, classification, concentration (enrichment), and characterization processes are all fabricated as needed onto a single substrate or layered stack of such substrates. By taking advantage of modern micro-machining capabilities, an entire suite of discrete laboratory aerosol handling and characterization techniques could be combined onto a single substrate, where they could be operated either serially or in parallel to perform a simultaneous characterization of the sampled aerosol. The ALOC is analogous to the integrated circuit, wherein a variety of discrete electronic (aerosol) components are combined onto a single chip to build-up complex electrical (aerosol characterization) systems. The performance of several of these analytic aerosol handling and characterization techniques would benefit by miniaturization (e.g., particularly the inertial techniques). By constructing arrays of identical parallel modules, it should be possible to reduce gas velocities that could give a quadratic reduction in pressure drop and consequently a quadratic reduction in power consumption. Sampling discrepancies would also be reduced; i.e., by virtue of their close proximity on the chip, each on-board characterization technique would be analyzing essentially the same aerosol sample.
It is an object of the invention to provide an aerosol diagnostic tool.
A further object of the invention is to provide a single device on which numerous aerosol characterization techniques may be carried out.
A further object of the invention is to provide a single apparatus that combines any of aerosol collection, classification, concentration (enrichment), and characterization processes.
Another object of the invention is to provide an aerosol lab-on-a-chip (ALOC) by advanced micro-machining capabilities wherein a suite of discrete laboratory aerosol handling and characterization techniques can be combined onto a single substrate or a layered stack of such substrates.
Another object of the invention is to provide an ALOC, where an entire suite of aerosol processing techniques can be operated either serially or in parallel to perform a simultaneous characterization of the sampled aerosol.
Another object of the invention is to provide an ALOC which is analogous to the integrated circuit wherein a variety of discrete aerosol (electronic) processing components are combined onto a single chip to build-up complex aerosol characterization (electrical) systems.
Another object of the invention is to provide an ALOC including arrays of identical parallel modules whereby gas velocities can be reduced which could give a quadratic reduction in pressure drop and consequently a quadratic reduction in power consumption.
Another object of the invention is to provide an ALOC whereby sampling discrepancies would be reduced, i.e., by virtue of their close proximity on the chip, each technique analyzes essentially the same aerosol sample.
Another object of the invention is to provide an ALOC that can be made sufficiently small and rugged to enable placement directly into harsh environments in which current laboratory equipment would not be operated.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention involves a single apparatus, formed on a substrate, or layered stack of such substrates, to collect, classify, concentrate, and characterize gas-borne particles. The invention described herein, provides a solution for an ideal aerosol diagnostic tool. The tool provides a variety of aerosol collection, classification, concentration (enrichment), and characterization processes are all fabricated, as needed, onto a single substrate or layered stack of such substrates, by well known advanced micro-machining techniques. The present invention, therefore, provides a method wherein an entire suite of discrete laboratory aerosol handling and characterization techniques can be combined onto a single substrate, or substrate stack, where they can be operated either serially or in parallel to perform a simultaneous characterization of the sampled aerosol. The ALOC reduces sampling discrepancies by virtue of their close proximity on the chip, each technique would be analyzing essentially the same aerosol sample. Gas-moving devices, such as pumps or fans, can be included to provide the gas throughput needed for the aerosol sampling and analysis in the absence of a moving gas stream. Use of such gas moving devices is necessary where insufficient gas flow exists in order to establish a flow of sufficient volume and velocity of gas through the characterization module(s) to ensure sampling an adequate number of particles to provide an accurate measurement. Electronic circuitry can also be fabricated onto the ALOC to provide for sensors, process control (valves, switches, etc.), signal processing, data analysis, and telemetry. The greatest advantage of the ALOC is the combination of a variety of aerosol processing and characterization techniques into a single, rugged, compact diagnostic that can provide a wealth of particle characterization data at relatively low cost.